One of the goals of plant genetic engineering is to produce plants with agronomically desirable characteristics or traits. The proper expression of a desirable transgene in a transgenic plant is one way to achieve this goal. Elements having gene regulatory activity, i.e. regulatory elements such as promoters, leaders, introns and transcription termination regions, are non-coding polynucleotide molecules which play an integral part in the overall expression of genes in living cells. Isolated regulatory elements that function in plants are therefore useful for modifying plant phenotypes through the methods of genetic engineering.
Many regulatory elements are available and are useful for providing good overall gene expression. For example, constitutive promoters such as P-FMV, the promoter from the 35S transcript of the Figwort mosaic virus (U.S. Pat. No. 6,051,753); P-CaMV 35S, the promoter from the 35S RNA transcript of the Cauliflower mosaic virus (U.S. Pat. No. 5,530,196); P-Rice Actin 1, the promoter from the actin 1 gene of Oryza sativa (U.S. Pat. No. 5,641,876); and P-NOS, the promoter from the nopaline synthase gene of Agrobacterium tumefaciens are known to provide some level of gene expression in most or all of the tissues of a plant during most or all of the plant's lifespan. While previous work has provided a number of regulatory elements useful to affect gene expression in transgenic plants, there is still a great need for novel regulatory elements with beneficial expression characteristics. Many previously identified regulatory elements fail to provide the patterns or levels of expression required to fully realize the benefits of expression of selected genes in transgenic crop plants. One example of this is the need for regulatory elements capable of driving gene expression in roots.
Root specific genes, i.e. genes whose RNA transcripts are expressed specifically or at higher levels in root tissue, have been reported previously in many species. While the protein-coding DNA sequence and the function of the related protein is often the subject of investigation, the non-coding regulatory elements of these genes may also prove useful when operably linked to a transcribable polynucleotide molecule where root specific expression in a transgenic plant is desirable. To identify regulatory elements capable of driving root specific gene expression in a transgenic plant, we investigated the regulatory elements for root specific genes. Of particular interest were regulatory elements from the rice RCc3 gene. This gene was reported to be expressed in a root specific manner (Xu Y, Buchholz W G, DeRose R T, Hall T C. Plant Molecular Biology 27: 237-248, 1995). We found that isolated regulatory elements for this gene, particularly the promoter and leader elements, provided good root specific expression of an operably linked transgene in a transgenic crop plant.